Power transformer monitoring using UHF sensors: installation and testing

External UHF couplers have been fitted to a 1000 MVA autotransformer as part of a project aimed at developing new transformer monitoring techniques. The couplers will supply valuable raw data from a transformer operating under normal service conditions. UHF signals were recorded while the transformer was re-energized and returned to load. Initially, some large discharges appeared, but these were short-lived. Background signal levels were low, indicating no significant interference problems. A small intermittent discharge signal was recorded and its characteristics are described. The possibilities for UHF monitoring of transformers are discussed, together with some of the remaining challenges.